Eric Sembrat's Test Bonanza

Human and animal societies are exemplars of complex adaptive systems. Through multiple interactions between society members, they dynamically organize themselves and integrate information over multiple scales, both above (environmental) and below (genetic, physiological) the individual level. In the past 25 years, researchers across a range of fields including statistical physics, network theory and behavioral ecology have made enormous progress in understanding the positive and negative consequences of these multi-scale, self-organizing coordination mechanisms. I will present key concepts in the field of collective animal and human behavior, and review recent results from both theoretical and empirical studies conducted in my laboratory on ant colonies, slime mold cultures and human crowds. In particular I will discuss the role of interactions between group members and with their environment, the mechanisms by which information is transferred by and integrated into a population, and the consequences of functional and dysfunctional group dynamics.

In the mid 60's, theoretical physicists came to the conclusion that a strong magnetic field could lead to a superconducting state where magnetism and superconductivity are interleaved on the nano-scale: tidal wave like domain walls spontaneously form in the superfluid order, trapping unpaired spins. Over the past 50 years, our theoretical understanding of this proposal has greatly advanced, yet we still have not found definitive experimental evidence of the modulated superconducting state (also known as the FFLO state, after the initials of the theorists who anticipated it). I will describe the current state of this search, with a particular focus on how experiments with ultracold atoms are about to find it.

Development of laser-based techniques to cool and manipulate trapped atoms led to a quantum revolution, with applications ranging from creation of novel phases of matter to realization of new tools for navigation and timekeeping. Because of their comparatively richer internal structure, molecules offer additional potential for quantum-controlled chemistry, quantum information processing, and precision spectroscopy. However, obtaining control over the rotational quantum state of trapped molecules, a prerequisite for most applications, has presented a significant challenge because of the large number of initial states typically populated and because of unwanted excitations generally occurring during optical manipulation. Using a single spectrally filtered broadband laser simultaneously addressing many rotational levels, we have optically cooled trapped AlH+ molecules from room temperature to 4 Kelvins, corresponding to an increase in ground rotational-vibrational state population from 3% to 95%. We anticipate that the cooling timescale can be reduced from 100 milliseconds to a few microseconds and that the cooling efficiency can also be improved. Our broadband cooling technique should also be applicable to a number of other neutral and charged diatomic species. Trapped AlH+, in particular, is a good candidate for future work on ultracold chemistry, coherent control and entanglement of rotational quantum states, non-destructive single-molecule state readout by fluorescence, and searches for time-variations of the electron-proton mass ratio.

Entangled polymers have been thoroughly studied since the 1940s at least....or so we thought. In the last decade particle velocimetry and other imaging methods, combined with rheology, have shown that some dramatic instabilities can occur in strongly sheared well-entangled polymer melts. I will discuss how some of these new observations (such as various shear banding phenomena and `fracture') can be understood in terms of the 'Standard Model' for entangled polymers, and highlight some of the current controversies in the area.

The history of drift-tube measurements of gaseous ion transport coefficients is reviewed, with an emphases on the contributions made by Dr. Gatland.  The use of experimental measurements of such coefficients in testing ion-neutral interaction potentials over wide ranges of internuclear separation is illustrated through recent tests of ab initio potentials.  Finally, the use of such data with recent theoretical advances is shown to have implications for ion-neutral reactions of importance in the ionosphere.

Coalescing binaries are among the most promising sources of gravitational waves for the advanced generation of ground based interferometers. Moreover they have been suggested as a possible progenitors of short gamma-ray bursts. The gravitational signal emitted in the late inspiral of such systems encodes the deformability properties of the neutron star, which depend on the behavior of matter in the stellar interior.

In this talk I will discuss how the detection of this signal can be used to extract information on the neutron star equation of state, and on the physics of the surrounding environment.

The concept of polariton is ubiquitous in the context of radiation-matter interaction. It refers to a generic quasi-particle resulting from the mixing of light with some kind of material excitation (e.g. a plasmon, phonon, or exciton). Cavity optomechanics offers an ideal system to study the coupling between trapped photons and the oscillations of a mechanical resonator. We can thus describe the coherent dynamics in terms of polaritonic excitations.

The role of dissipation mechanisms adds another layer of complexity to the problem. In particular, the photon and the mechanical phonon are coupled to reservoirs with different temperatures. This situation opens up the possibility to investigate thermodynamics at the quantum level as well as engineer heat engines at the nanoscale.

Striding bipedalism evolved over 230 million years ago in the ancestors of dinosaurs. Predatory dinosaurs (Theropoda) gave rise to tyrannosaurs and velociraptors, but also to birds, which survived the end-Cretaceous extinction. Fossilized skeletons and trackways offer unique, if static, evidence of ancient species. We seek to integrate data from living avians with the fossil record to understand theropods as living, moving organisms, as well as broader patterns of locomotor evolution along this lineage. I will first present a brief overview of X-ray Reconstruction of Moving Morphology, a 3-D method of skeletal motion analysis that we developed at Brown. I’ll then present animations, data, and questions from two studies using an XROMM approach. First, a six degree of freedom description of joint kinematics in guineafowl reveals a surprising amount of long-axis rotation at the hip and knee. Despite the limb’s superficially planar appearance, rotations about long bone axes are critical to maneuvering and steady locomotion in modern birds. When and why did this mechanism of 3-D limb control evolve? Second, we combine XROMM-based foot motion of birds walking through deformable substrates with Discrete Element Method (DEM) simulation to explore footprint formation. Modeling results from ‘virtual bedding planes’ show dramatic changes in track shape with depth, which could be easily misinterpreted if exposed as fossils. Linking DEM and XROMM techniques fosters a new perspective on the ‘birth’ of track morphology, the origin of footprint diversity, and inferences of trackmaker anatomy and behavior.

Hydrodynamics is the theory describing collective behaviors of fluids and gases. It has a very long history and is usually considered to belong to the realm of classical physics. In recent years, it has been found that, in many cases, hydrodynamics can manifest a purely quantum effect --- anomalies. We will see how this new appreciation of the interplay between quantum and classical physics has emerged, unexpectedly, through the idea of gauge/gravity duality, which originates in modern string theory. I will briefly mention the possible relevance of the new findings to the physics of the quark gluon plasma.